1. Field of the Invention
The present invention relates to a wire bonder that performs bonding by spreading a wire between the bonded component, in the form of a semiconductor component (IC chip), and a lead, and more particularly, to a bonding misattachment detection apparatus and that detection method in a wire bonder able to detect misattachment when, for example, the wire breaks or there is a defective connection (referred to as misattachment) in the case wire that is spread between, in particular, an IC chip and a lead, is not connected.
2. Description of the Prior Art
In the case of performing bonding between the pad of an IC chip and a lead using this type of wire bonder of the prior art, the wire is held with a bonding tool in the form of a capillary provided on the end of a bonding arm, which is then brought in contact with the surface of the target pad or lead, followed by crushing of a portion of the wire, on which a ball was formed on the end, using said capillary to perform thermocompression bonding. There are also cases in which ultrasonic vibrations are simultaneously applied to the end of the wire at this time.
The following provides an explanation of this wire bonding process referring to FIG. 1. When wire bonding is to be performed on the pad (electrode) on IC chip 25 placed on bonding stage 26, capillary 7, through which wire 9, having a ball formed on its end, is passed, is positioned by movement of an XY table based on the information from a photographic apparatus not shown. Following this positioning, capillary 7 is lowered as indicated in steps (1) through (3) of FIG. 1 to crush the ball onto the above-mentioned pad and perform thermocompression bonding.
In this process, the bonding arm is lowered and moved at high speed from step (1) to step (2), and moved at low speed from step (2) to step (3). Clamp 8a is open at this time. Next, when connection to the 1st bonding point is completed, bonding arm 1 is raised upward (direction of the Z axis) as indicated in FIG. 1 with clamp 8a remaining open from step (3) to step (4). Wire 9 is then pulled out with clamp 8a still open following a prescribed loop control as indicated in step (5). This is then connected to the 2nd bonding point in the form of lead 27 as indicated in step (6).
Following this connection, clamp 8a closes after wire 9 has been pulled out by a prescribed feed amount f from the end of capillary 7 as indicated in step (7). While still in this state, wire 9 is cut as indicated in step (8) in the process of bonding arm 1 further rising to a prescribed height. A ball is again formed on the end of the wire using an electric torch followed by returning to the state of step (1) with clamp 8a open. Wire bonding is thus performed by this series of steps.
In the case the wire should happen to break and so forth in this series of steps for performing the above-mentioned wire bonding, defective bonding will result. Thus, it is necessary to detect such broken wires and so forth. A known example of a method used to detect broken wires of the prior art is disclosed in Japanese Patent Laid-Open No. 50-68271.
In this method, wire bonding is performed utilizing the timing of a momentary event in which clamp 8a closes and only capillary 7 rises as indicated in step (7) of FIG. 1. After insulating clamp 8a from the wire bonder in advance, a voltage is applied between clamp 8a and lead 27 so that clamp 8a is positive and lead 27 is negative. By taking advantage of the momentary closing of clamp 8a and rising of capillary 7 in this state, the continuity is measured between clamp 8a and lead 27 by producing a timing signal for testing continuity. Evaluation of broken wires is then performed by running this timing signal and continuity signal into both inputs of an AND circuit. In other words, when both the timing signal and continuity signal are applied to the AND circuit, an output signal is produced from the AND circuit indicating that bonding work is being performed normally. When only the timing signal is applied to the AND circuit and an output signal is not produced from the AND circuit, this indicates that a broken wire has been encountered during wire bonding.
3. Problems that the Invention is to Solve
However, in the method of the prior art for detection of broken wires in wire bonders, since broken wire detection is performed by applying a voltage between clamp 8a and lead 27 so that clamp 8a is positive and lead 27 is negative, application of such a voltage can damage bonded components such as semiconductor components (IC chips) featuring reduced thickness and increased level of integration in recent years. In addition, there is also the risk of these components being damaged due to generation of static electricity.
In addition, the method of the prior art also has the disadvantage of it being necessary to determine the polarity and so forth of the pad of the semiconductor component (IC chip), thus limiting the types of IC chips to which this method can be applied. Furthermore, since the detection method of the prior art requires screening of those IC chips that can be detected, it has the additional disadvantage of preventing improvement of work efficiency.
In addition, when the detection method of the prior art was applied to semiconductor components such as metal-oxide semiconductor integrated circuits (MOS integrated circuits), it is difficult to perform detection using the conventional direct current detection method. In addition, since it is also difficult to set the detection level with this method, the detection method of the prior art has the additional disadvantage of being impractical in the case of the above-mentioned components.